Fluorinated analogs of norepinephrin have been synthesized using the photochemical procedures developed earlier. Studies with these analogs, and fluorinated analogs of tyramine, dopamine, melatonin, and serotonin previously prepared, have revealed important information concerning the mobility of serotonin stored in human platelet vesicles and the use of F19 NMR spectroscopy as a probe for molecular motion, the conformational requirements for norepinephrin in interaction with alpa and beta adrenergic receptor systems, and the role of phenol pK and lipophilicity in determining activity of biogenic amines.